Jersey Barriers are designed to redirect a crash, using the vehicle's momentum to absorb the impact and slide the vehicle up parallel along the side of the barrier to prevent a rollover. An F-Shape barrier has the same 3-inch-high base, but features a side that slopes 10 inches above the pavement-three inches less than the side slope of the Jersey Barrier—and is thus able to better absorb proportional impacts from smaller chassis to prevent a rollover. Jersey Barriers as well as other barrier designs, including constant slope, single slope, and vertical are acceptable for adequately preventing roll-overs.
The start of a barrier is dangerous because with a head on crash the shape of the barrier is not effective in limiting crash momentum or preventing roll-overs. Typical solutions include Impact attenuators, crash cushions, water filled attenuators, and sand filled Fitch barriers.
Water-filled attenuators consist of containers filled with water to absorb impact energy. They are typically not anchored to the ground, and therefore benefit from easy deployment and relocation using barrier transfer machines and cranes. They are non-redirective, meaning they do not deflect vehicles that impact the side back into the roadway.
A Fitch barrier consists of sand-filled plastic barrels, usually yellow colored with a black lid. Fitch barriers are often found in a triangular arrangement at the end of a guard rail between a highway and an exit lane (the area known as the gore), along the most probable line of impact. The barriers in front contain the least sand, with each successive barrel containing more, so that when a vehicle collides with the barrels they shatter, the kinetic energy is dissipated by scattering the sand and the vehicle decelerates smoothly instead of violently striking a solid obstruction, reducing the risk of injury to the occupants.
Crash cushions are constructed of multiple segments, which crumple into each other when collided with to absorb the impact. Their main benefit is in their reusability; these attenuators can automatically return to their original position after a crash.
Impact attenuators are tested and classified based on the maximum speed of a vehicle during a collision for which the attenuator is designed. Therefore impact attenuators may not be effective for speeds or weights that are over the classification.
Most impact attenuators are completely destroyed by a single crash and the danger the now damaged impact attenuator is designed to protect could be exposed for months while the parts are replaced.
Also, the intense deceleration during a crash into an impact attenuator is still very dangerous to people and will surely damage a vehicle.